This invention relates to control apparatus for electric motors and more particularly to a control apparatus for an inverter-driven electric motor, which digitally controls the motor by means of a digital computing circuit.
There has been an increasing demand for the speed adjustable electric motors as a means of increasing the functional efficiency of electric motors as well as equipment incorporating electric motors, and many different attempts have been made to ensure a greater control accuracy. Recently, microcomputer-controlled high-efficiency equipment has been made available, and also inverters incorporating high switching speed power devices have been made available. In addition, there has been a trend toward making the speed of electric motors variable by means of pulse width modulation or choppers and other control methods employing the pulse width modulation of the unequal pulse type. However, according to these known control methods there is provided in all cases a circuit for each of the controlled systems and consequently if a microcomputer is used, a variety of controls will be required for effecting an overall control of the electric motor. In the case of apparatus in which the motor controls are effected separately and the discrete control circuits provided for the individual controlled systems are simply combined together as mentioned previously, the systematic mutual actions among the controlled systems have not been brought into effect adequately, and it has been difficult to ensure a precise control. Another disadvantage is that the circuits become complicated undesirably.